Antibacterial Activity of Silver Nanoparticles Isolated from Cow's Milk, Hen's Egg White and Lysozyme: A Comparative Study

The aim of the present study is to evaluate the antibacterial activity of biosynthesized silver nanoparticles (AgNPs) with the dietary, nontoxic, eco-friendly biological materials such as raw and pasteurized cow's milk, egg white and lysozyme. The chosen organisms are clinically important, and hence its in vitro evaluation gains significance in the field of medicine. The AgNPs were characterized by UV-visible spectroscopy which revealed surface plasmon absorbance peaks, ranging between 400 and 450nm. Fourier transform infrared spectroscopy showed the presence of characteristic C=O and O-H bonds. Transmission electron microscopy revealed spherical particles ranging between 20 and 200 nm. Scanning electron microscopy-energy-dispersive spectroscopy revealed peak at 3keV confirming the presence of AgNPs. SDS-PAGE analysis further ascertained this with the absence of some protein bands in AgNPs solution as against their respective controls which could indicate its role during the synthesis. The comparative antibacterial activity was determined by well diffusion method. Effective inhibition zones obtained by AgNPs synthesized from the pasteurized milk were 12mm +/- 0.7 against Escherichia coli DH5 alpha and Bacillus subtilis, 14.5mm +/- 0.5 against Pseudomonas alcaligenes and Staphylococcus aureus, 15mm +/- 0.7 against Bacillus cereus. The percentage inhibition displayed by AgNPs from pasteurized cow's milk was 48%, 58%, 65.9%, 85.7% and 68.2% against the growth of E. coli DH5 alpha, P. alcaligenes, S. aureus, B. subtilis and B. cereus, respectively, which was significant when compared to the inhibition profiles of AgNPs obtained from other sources such as raw milk, lysozyme and egg white.